Lubricant coated formable metal article



United States Patent 3,258,319 LUBRICANT COATED FORMABLE METAL ARTICLE John J. Cox, Jr., Wilmington, DeL, assignor to E. I. du

Pont de Nemours and Company, Wilmington, DeL, a

corporation of Delaware No Drawing. Filed Nov. 23, 1962, Ser. No. 239,822

6 Claims. (Cl. 29-195) This invention relates to an improved formable metal article. In particular, this invention relates to a formable article comprising a metal substrate having an improved metal=working lubricant coating thereon. In addition this invention relates to an improved process for forming a metal article.

In cold-working operations for forming metals, such as drawing, stamping, coining, rolling, forging, swaging, extruding and modifications thereof, where metal is formed by exertion of pressure upon the metal by a metalworking tool, a considerable amount of the total work expended to achieve the desired resultant shape of the metal is used to overcome the friction between the metal and the metal-working tool. Metal articles coated with several types of metal-working lubricants have been used with varying degrees of success in reducing the friction in metal forming operations. However, a need exists for a more readily formable metal article, that is, a metal article treated in such a manner so as to considerably reduce the amount of Work required to overcome friction in a metalworking operation.

An object of this invention is to provide a readily formable metal article. Another object is to provide a formable article comprising a metal substrate having an improved metal-working lubricant coating thereon. A further object is to provide an improved process for forming a metal article.

These and other objects are attained by a coated metal article having substantial bulk, the dimensions of which are alterable by a cold forming operation, said article having a coating thereon which comprises 50-95% by weight of petroleum wax and -50% by weight of a normally solid polymer containing at least about 60% by weight of an olefin having 2-4 carbon atoms.

The term forming, as used herein, refers to any cold metal-working process, including the so-called primary working processes whereby articles such as ingots, billets, or powder compacts are converted to mill products such as bars, beams, plates, tubes, rods, strips, sheets and the like. Primary working processes include cold rolling, cold forging, cOld swaging, cold drawing, cold extrusion and modifications thereof. Forming also encompasses the so-called secondary working processes whereby mill product articles, usually plates or sheets are formed into useful articles of manufacture. Secondary working processes include stamping, drawing, coining and other such forming operations. The process used should be operated at a temperature below the melting point temperature of the petroleum wax to avoid liquification thereof. Generally, operation at a temperature of below about 125 F. is satisfactory.

All metals which are formable by cold metal-working processes are usable in this invent-ion. Some of these metals are titanium, zirconium, vanadium, tantalum, chromium, molybdenum, iron, nickel, platinum, copper, silver, gold, zinc, cadmium, aluminum and the formable alloys including brass, bronze and the like and the ferrous metal alloys such as the various carbon and stainless steels. Particularly adaptable for use in the practice of this invention are formable sheets which comprise a ferrous metal substrate having a ferritic chromium containing alloy coating. Such alloy coated products may be produced by various methods familiar to the art, for example, by the adhesive bonding or cladding of a chromium alloy coating onto the ferrous metal substrate, or by chromium diffusion-coating processes.

Any normally solid polymer containing at least about 60% by weight of an olefin having 2-4 carbon atoms may be used in this invention.

As used herein, the term normally solid is synonymous with non-liquid at room temperature (i.e. about 25 C.). Thus, a polymer which has the physical characteristics commonly associated with a grease may be used in this invention. However, it is generally preferable to use a polymer which has a greater degree of solidity than a grease. In other words, the preferred polymers are those which have the physical characteristics of soft waxes, hard waxes, soft resins, hard resins, and so forth.

Molecular weight and degree of crystallinity are two important variables which affect the solidity of the polymer. In the case of polypropylene, for example, the polymers which have a fairly high degree of crystallinity, such as the isotactic polymers, and which have a molecular weight of at least about 1,000 possess the preferred degree of solidity. The amorphous polymers such as atactic polypropylene do not have a specific minimum molecular weight which marks a distinct separation between normally solid and normally non-solid phases. Generally, the liquid atactic propylene polymers are those with molecular weights below about 300 to 500. While the degree of solidity of the polymer increases 'with increasing molecular weight, even atactic polypropylene with a molecular weight of several thousand exhibits cold flow. However, atactic polypropylene with a molecular weight of at least about 1,000 usually is sufiiciently solid to be useful in this invention. In other words, the lower limit of the molecular weight depends on the particular polymer employed. There is no upper limit as to the molecular weight of the polymers used in this invention.

The polymers of this invention include the homopolyrners of olefins containing 2-4 carbon atoms, that is, polyethylene, polypropylene, polisobutylene, etc., and copolymers of such olefins with other copolymerizable monomers,for example, vinyls such as vinyl acetate and vinyl chloride, a'lkyl acrylates and methacrylates, carboxylic acids such as methacrylic acid, and other copolymerizable monomers including styrene and acrylonitrile. The term olefin refers not only to those hydrocarbons having one olefinic double bond, but also to the dienes such as butadiene. A mixture of two or more of these olefin polymers may be used if desired so long as the metal working lubricant contains 550% by weight of at least one of the described polymers. It is essential that the polymer used be normally solid and it must contain at least about 60% by weight of an olefin having 2-4 carbon atoms. Particularly preferred species of this invention are those employing a propylene polymer or an ethylene/ vinyl acetate copolymer.

Some of the polymers of this invention are not completely compatible with petroleum wax. Compatibility is a function of both the type of polymer used and the amount of copolymer blended with the wax. In the case of ethylene/ vinyl acetate copolymers, for example, blends of 5095% by weight of petroleum wax and 550% of a copolymer containing either 15-25% or 33-40% of vinyl acetate, have a haze point which varies from about 5 C. to 30 C. or more above the melting point of the wax depending on the particular composition of the blend. It is not essential that the wax-polymer blends used in the practice of this invention be completely compatible. Thus, ethylene/vinyl acetate copolymers containing 15-40% by weight of vinyl acetate (i.e., about 6085% ethylene) are useful in this invention. However, it is generally preferable to use more compatible blends, in particular those in which the copolymer contains from 25-33% by weight of vinyl acetate. Vinyl acetate content of the copolymer may be determined by infrared analysis or by saponification number determination.

The various methods of preparation of the polymers used in this invention are well known to those skilled in the art. The particular process employed is not critical, thus any convenient procedure can be used, for example as described in Sittig, Polyolefin Resin Processes, Gulf Publishing Company, Houston, 1961, and also in U.S.P. 2,153,553, U.S.P. 2,200,429, U.S.P. 2,274,749, U.S.P. 3,051,690; and elsewhere.

The term petroleum wax as used herein refers to both paraflin and microcrystalline waxes. Paraffin wax is a mixture of solid hydrocarbons derived through the fractional distillation of petroleum. After purification paraffin wax contains hydrocarbons that fall within the formulas C H C H It is a colorless, hard and translucent material having a melting point of about 125 165 F. Microcrystalline wax is also obtained through petroleum distillation. It differs from parafiin Wax in having branched hydrocarbons of higher molecular weights. It isconsiderably more plastic than paraffin wax and has a melting point of about ISO-200 F.

The petroleum wax-polymer blends which are used in this invention contain from about 50% to 95% by weight of petroleum wax and from about to 50% by weight of polymer. These blends may be prepared in any convenient manner known in the art such as shown in U.S.P. 2,290,392, U.S.P. 2,290,393, U.S.P. 2,504,270, U.S.P. 2,595,911 and British Patent 887,417.

In the practice of this invention, a metal article is coated with the wax-polymer blend by any suitable procedure. For example, a metal article may be dipped into a hot melt of such a blend, or a solvent solution of the blend may be prepared which can be used to coat the metal by dipping, spraying or brushing techniques. To insure adequate adherence of the coating to the metal= article, it is usually referable to preclean the metal article to remove foreign matter such as grease, grit and the like. The required thickness of the coating depends upon the specific operating conditions, such as the particular metal article used, the forming process employed, and so forth. Therefore, the amount of the wax-polymer blend to be applied to the metal article is determined by trial and practical experience, however, for most cases, the coating should be at least 1 mil thick. After the coating is thus applied, the metal article may be formed as desired.

The primary purpose of the coatings of this invention is to serve as a metal-working lubricant. In normal industrial practice, the coating is removed from the article after the article has been formed. One convenient manner by which the wax-polymer coatings may be removed is by first subjecting the coated articles to temperatures slightly above the melting point of the petroleum wax and permitting the coating to flow off of the article; subsequently, any of the wax-polymer which remains on the article may be burned off. The wax-polymer blends of this invention are soluble in several common solvents such as benzene, toluene, xylene, and trichlorethylene, and therefore these coatings may also be easily removed by a solvent washing procedure. Before and after forming, care should be taken to avoid baking the coating or otherwise subjecting the coating to conditions which would promote crosslinking of the polymer chains in the waxpolymer blend to thereby insolubilize the coating. Avoidance of a relatively thin coating, i.e., less than 1 mil thick, and elevated temperatures, usually prevents such crosslinking and thus insures that the coating will be readily removable.

The advantages obtained by this invention are illustrated by the following series of examples. Two standard tests ar used in these examples:

OLSEN CUP TEST This test is conducted in accord with ASTM 20, Part II, 398. A lubricated metal blank of about four square 4. inches is clamped between a die and ball of given radius. The ball is hydraulically forced through the blank causing it to stretch. To compare the lubricating effect of vari ous coatings, several runs are made with different coatings using the same die, ball, and type of metal blank. Since the die, ball, and metal blank are constant, the depth of the cup to rupture is dependent on the effectiveness of the lubricating coating.

ERICKSEN DEEP DRAW TEST In conducting this test, a circular lubricated metal blank of a given diameter is hydraulically clamped between a punch and die. The punch forces the metal through the die and a cup is thereby formed. This cup is then redrawn with a smaller diameter punch and die. Variables measured as a function of the lubricating effect of the coating are: the force required to make both draws, which should be a minimum; and, the depth to which the second draw is made prior to rupture, which should be a maximum. Further details of this test are given in the Metals Handbook, page 129, 1948 Edition, published by The American Society for Metals. In the following examples, the hydraulic clamping pressure in each instance was 2,420 pounds.

The following examples are intended only to illustrate this invention and are not intended to impose any limitations on the scope thereof.

Example 1 This example shows the performance of two standard metal-working lubricants commonly used heretofore.

In all the tests shown in this example and in Examples 2-5 shown hereinafter, SAE 1008 aluminum-killed drawing steel, 0.026 inch thick, was used. In each test, the steel was treated, prior to coating, as follows: The steel samples were first degreased in trichlorethylene vapor, and then pickled in 6 N HCl for one minute. Pickled samples were thoroughly washed in running water, and then rinsed in acetone and forced air dried.

For this example, different samples were coated with tallow and graphite grease. Samples with a 72 mm. diameter were deep drawn in an Ericksen machine. The sample coated with tallow required an average drawing force of 3660 lbs./in. for the first draw while the sample coated with graphite grease required an average drawing force of 3510 lbs./in. for the first draw. Other samples at least mm. square were cupped to rupture in an Olsen machine. The sample coated with tallow gave an average cup depth of 423 mils, and the sample coated with graphite grease gave an average cup depth of 418 mils.

In view of the above data, tallow coated samples were used as the standard of comparison in the Olsen Cup Test in the following examples, while the graphite grease coated samples were used as the standard of comparison in the Ericksen Deep Draw Test.

Example 2 Two solvent solutions of ethylene/vinyl acetate-wax blends were prepared as follows: 45 parts by Weight of a blend consisting of 30% by weight copolymer and 70% wax was dissolved in 55 parts of toluene; the second solution was prepared by dissolving 40 parts of a blend consisting of 70% copolymer and 30% wax in 60 parts toluene. The copolymer used in both solutions was an ethylene/ vinyl acetate copolymer having a vinyl acetate content of 28%, by weight, and a melt index of 15. The two solutions were maintained at temperatures of 60 C. and 70 C. respectively. Panels of the SAE 1008 aluminum-killed drawing steel, described above, having a surface area of 90 square mm. were treated as shown in Example 1 and were coated by dipping into the solutions and then dried to remove all toluene. The blend containing 30% copolymer gave an average coating thickness of 2.2 mils. The blend containing 70% copolymer gave an average coating thickness of 1.4 mils. The samples were evaluated by the Olsen Cup Test method, giving the results tabulated in Table I. All figures in Table I represent an average of 3 tests.

TABLE I Coating composition: Olsen cup depth, mils Tallow 423 i 3 30% copolymer-70% wax "455:2 70% copolymer30% wax "439:6

Table I shows the significant improvement over standard lubricants, which is obtained by steel coated with a blend of 30% ethylene/ vinyl acetate copolymer and 70% paraffin wax.

Example 3 Circular samples of the treated steel described in Example 1, having diameters of 72 mm. were dipped in the coating solutions described in Example 2. These samples were subjected to the Ericksen Deep Draw Test, the results of which are summarized in Table II. All figures shown in Table II represent an average of 5 tests.

As shown in Table II, the steel coated with the blend of 30% ethylene/vinyl acetate copolymer-70% paraffin TABLE II Force to Draw, lbJin.

Coating Comp. Fedmw with 26mm. punch Drawwith 33 mm. punch containing by weight of an ethylene/vinyl acetate having a vinyl acetate content of 28% by weight and a melt index of 15. This solution was maintained at 70 C. The average coating thickness was 1.5 mils. For Test 4, the panels were not coated. For Test 5, panels were coated by dipping in a hot melt of parafiin wax. These wax coatings were thick and nonuniform. In all of these tests, the panels were evaluated by the Olsen Cup Test method, the results of which are shown in Table III. All results shown in Table III represent an average of 3 tests.

TABLE III Test Coating Composition Olsen Cup Depth, Mils 30% copolymer-70% wax 443 70% copolymer-30% Wax 402 Copolymer only 399 Uncoated 359 Wax only: This material cracked, spalled and adhered to the punch, and therefore did not give significant results.

Rupture, Average Depth, mm.

Graphite Grease 3, 5101119 4, 520:1:171 25.5:h0.9.

30% copolymer-70% wax... 3, 24:35:47 3, 8505;82

70% copolymer-30% wax-.. 3, 662:1;99

(ruptured) Did not rupture, all drew greater than mm.

wax gave a decided improvement over the steel coated with a standard lubricant, requiring 265 lb./in. less force for the first draw and 670 lb./in. less force for the redraw, and giving a cup depth of over twice that obtained with the graphite grease, and without rupture.

The steel coated with the blend of 70% copolymer and 30% paraflin wax ruptured on the first draw. In other words, metal coated with such a blend is actually not as satisfactory as metal coated with standard lubricants known in the art, and hence, is outside of the scope of this invention.

Example 4 Example 3 is repeated using in place of the aluminumkilled drawing steel shown therein, degreased circular samples of a ferritic chromium-containing alloy diffusion coated steel 0.026 inch thick having a diameter of 72 mm. Similar results are obtained.

Example 5 Example 3 is repeated using in place of the ethylene/ vinyl acetate copolymer shown therein, polyisobutylene having a molecular weight of about 10,000. Similar results are obtained.

Example 6 In all of the tests of this example SAE 1008 aluminum-killed drawing steel 0.020 inch thick was used. Panels of this steel were prepared by degreasing in trichlorethylene vapor. For Test 1, panels of the prepared steel were coated by dipping into the solution of 30% copolymer and 70% wax described in Example 2 giving an average coating thickness of 1.5 mils. For Test 2, panels were coated by dipping into the solution of 70% copolymer and 30% wax described in Example 2 giving an average coating thickness of 1.5 mils. For Test 3, panels were coated by dipping into a toluene solution The comparative data of Table III illustrate that the copolymer-wax blends of this invention give an unexpected improvement over the use of copolymer alone, wax alone, and also over the use of copolymer-wax blends containing greater than 50% by weight of copolymer.

Example 7 Two solvent solutions of paraffin wax-polypropylene were prepared as follows: 45 parts by weight of a blend consisting of 10% by weight of an atactic polypropylene having a molecular weight of ca. 6,000 and 90% paraffin wax was dissolved in parts by weight of toluene at 70 C.; the second solution was prepared by dimolving 45 parts of a blend consisting of 30% by weight of an atactic polypropylene having a molecular weight of ca. 6,000 and 7 0% by weight of parafiin wax in 55 parts of toluene at 60-70 C. Panels of the SAE 1008 aluminumkilled drawing steel, described in Example 1 having a surface area of 90 square mm. were treated as shown in Example 1 and were coated by dipping into the solutions and then dried to remove all toluene. The thickness of the coatings obtained thereby, varied from 1.1 to 1.5 mils as between different panels.

These coated panels were evaluated by the Olsen Cup Test method, giving the results tabulated in Table IV. All figures in Table IV represent an average of 3 tests.

TAB-LE IV Coating composition: Olsen cup depth, mils Tallow 42313 90% wax-10% atactic polypropylene (M.W.

6,000) 448:6 wax-30% atactic polypropylene (M.W.

Example 8 Two solvent solutions of parafiin wax-polypropylene were prepared as follows: 45 parts by weight of a blend TABLE VI Force to Draw, llo./in.

Ru ture Avera e Test Coating Composition l eptli, mm. g

, Draw with Redrawn with 33 mm. punch 26 mm. punch 1 Graphite Grease 3, 510:1;119 4, 520:|;l71 25.5;l;0.0.

2 70271; gag-3835 Ataetic Polypropylene 3, 4355;43 4,350=l=147 35.1i2.6. a 707 'wax so f Atactio Pol ro lene 3,14'i68 4,400 4 ii/Lw. 12,006 yp Dy a $175 7 E5 1 4 70% Wax-30% lsotaetlc Polypropylene 3, 335=|=25 4, 1005:1310 All drew greater than (M.W. 100,000). 50 mm.

consisting of by weight of an atactic polypropylene having a molecular weight of ca. 12,000 and 90% paraffin wax was dis-solved in 55 parts by weight of toluene at 60- 70 C.; the second solution was prepared by dissolving 45 parts of a blend consisting of 30% by weight of an atactic polypropylene having a molecular weight of ca. 12,000 and 70% by weight of paraffin wax, in 55 parts toluene at 6070 C. Panels of the SAE 1008 aluminum-killed drawing steel, described in Example 1 having a surface area of 90 square mm. were treated as shown in Example 1 and were coated by dipping into the solutions and then dried to remove all toluene. The thickness of the coatings varied from 1.1 to 1.5 mils between panels. These coated panels were tested by the Olsen Cup Test method, giving the results shown in Table V. All figures in Table V represent an average of 3 tests.

TABLE V Coating composition: Olsen cup depth, mils 90% wax-10% atactic polypropylene (M.W. 12,000) 440:21 70% wax-30% atactic polypropylene Example 9 Circular samples of the SAE 1008 aluminum-killed drawing steel described in Example 1, having diameters of 72 mm., were treated as shown in Example 1. For Test 1 of this example, samples of this treated steel were 'coated with graphite grease to provide a standard of comparison with the following tests. For Test 2, steel samples were coated by dipping in the solution of 70% paraffin wax and 30 actactic polypropylene (molecular weight of 6,000) described in Example 7. For tests, steel samples were coated by dipping in the solution of 70% paraffin wax and 30 atactic polyropylene (molecular weight of 12,000) described in Example 8. For Test 4, steel samples were coated by dipping into a solution of parts by weight of a blend consisting of 70% paraflin wax and 30% of an isotactic polypropylene having a molecular weight of ca. 100,000, dissolved in 85 parts of toluene at 110 C. All of these coated samples were evaluated by the Bricksen Deep Draw Test, the results of which are shown in Table VI. The results shown in Table VI represent an average of 5 tests.

Other nonmally solid polymers containing at least 60% by weight of an olefin having 2-4 carbon atoms, including polyethylene, ethylene/ethyl acry-late copolymers, isobu-tylene/styrene copolymers, poly-butadiene, butadiene/ styrene copolymers, and the like, give similar results.

I claim:

1. A coated metal article having substantial bulk, the dimensions of which are alterable by a cold forming operation, said article having on its surface a metal working lubricant coating comprising to 95% by weight of petroleum wax and 5 to 50% by weight of a normally solid polymer containing at least by weight of an olefin having 2 to 4 carbon atoms.

2. The article of claim 1 wherein the said polymer is an ethylene/vinyl acetate copo-lymer containing 6085% by weight of ethylene.

3. The article of claim 1 wherein the said polymer is an ethylene/vinyl acetate copolymer containing -75 by weight of ethylene.

4. The article of claim 1 wherein the polymer is polypropylene.

5. A formable article having substantial bulk, the dimensions of which are alterable by a cold forming operation comprising a ferrous metal substrate having a ferritic chromium-containing alloy coating, and having a metal Working lubricant coating superposed thereon which comprises 5095% by weight of petroleum wax and 550% by weight of a normally solid polymer containing at least 60% by weight of an olefin having 2-4 carbon atoms.

6. The article of claim 5 wherein the polymer is an ethylene/vinyl acetate copolymer containing 65-75% by weight of ethylene.

References Cited by the Examiner UNITED STATES PATENTS 2,530,838 11/1950 Orozco 7242 X 2,648,643 8/1953 Adams et al 260-28.5 3,025,167 3/1962 Butler 260-28.5 3,078,237 2/1963 Creech et al 25259 X 3,080,330 3/1963 Rudel et a1 25259 X 3,084,128 4/1963 Stillwagon 117-132 3,117,101 1/1964 Moyer 117168 X RICHARD D. NEVl-US, Primary Examiner.

R. S. KENDALL, Assistant Examiner. 

5. A FORMABLE ARTICLE HAVING SUBSTANTIAL BULK, THE DIMENSIONS OF WHICH ARE ALTERABLE BY A COLD FORMING OPERATION COMPRISING A FERROUS METAL SUBSTRATE HAVING A FERRITIC CHROMIUM-CONTAINING ALLOY COATING, AND HAVING A METAL WORKING LUBRICANT COATING SUPERPOSED THEREON WHICH COMPRISES 50-95% BY WEIGHT OF PETROLEUM WAX AND 5-50% BY WEIGHT OF A NORMALLY SOLID POLYMER CONTAINING AT LEAST 60% BY WEIGHT OF AN OLEFIN HAVING 2-4 CARBON ATOMS. 